Air springs, or pneumatic suspension devices, have long been used to isolate road disturbances from a vehicle, seat, or cab. An air spring, as part of a vehicle's suspension, supports the vehicle's load or mass at each axle. Typically, each axle of a vehicle associated with an air spring supports the mass component or load carried by the axle. In addition, there may be ancillary air springs that support driver comfort in and around the driver's compartment, or cab. In an air spring, a volume of gas, usually air, is confined within a flexible container. As an air spring is compressed (jounce travel), the pressure of the gas within the air spring increases; and as an air spring extends (rebound travel), the pressure of the gas within the air spring decreases. Road disturbances are mainly absorbed by this compression and extension of the air springs as a function of work (w=∫F·dx). Air springs are often engineered to have a specific spring rate or spring constant, thereby controlling jounce and rebound characteristics for the desired application and for comfort.
Elastomeric articles such as air springs may undergo countless cycles between compression and extension, and must be flexible and durable. Over time and under operational stresses, the material properties of an airsleeve will change. Eventually, cracks may form and become sufficiently large so that the integrity of the airsleeve is challenged, requiring replacement.
Typically, the air spring bellows or airsleeve is made of cord-(fabric or metal) reinforced rubber compositions, which may be natural or synthetic materials. Unsaturated, chlorinated rubber such as neoprene, which is sometimes referred to as chloroprene rubber (CR), is often used due to its relatively low compression set, good resilience and abrasion resistance.
Saturated chlorinated polyethylene (CPE) has been used in various automotive and industrial rubber parts for its properties of heat, weather, and oil resistance. Commercially available from Dow Chemical Company under the tradename TYRIN®, CPE has been used in automotive wire and cable jacketing, hose and tubing, and industrial hoses. Product literature for TYRIN® CPE states that the molecular saturation of the CPE requires the use of vulcanization systems other than conventional sulfur systems. Furthermore, particular care must be taken in the selection of additives when compounding CPE, because additives that are beneficial in one cure system can be detrimental in another.
There remains a need in the market for compositions for airsleeve having improved properties, including shorter cure cycle, improved filler dispersion, and improved resistance to cracking and flex fatigue.